Patient-specific total hip arthroplasty

ABSTRACT

Disclosed herein are systems and methods for performing total hip arthroplasty with patient-specific guides. Pre-operative images of a pelvic region of a patient are taken in order to predefine the structure of the guides and corresponding implants. From the obtained image data an insertional vector for implanting an acetabular implant or component into an acetabulum of the patient is determined, wherein the insertional vector is coaxial with a polar axis of the acetabular component. Also from the obtained image data, a superior surface of the guides and implants can be shaped to match the acetabulum of the patient. A nub portion extending outwardly from the superior surface of the guides and implants is shaped to substantially match the shape of a fovea of the acetabulum. A guide portion of the guides forming a slot has a longitudinal axis coaxial with the determined insertional vector of a corresponding acetabular component.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/277,208 filed Sep. 27, 2016, which is a continuation of U.S.patent application Ser. No. 14/575,403 filed Dec. 18, 2014, now U.S.Pat. No. 9,474,615, which is a continuation of U.S. application Ser. No.13/163,037 filed Jun. 17, 2011, now U.S. Pat. No. 8,932,299, whichclaims the benefit of the filing date of U.S. Provisional PatentApplication No. 61/356,324 filed Jun. 18, 2010, the disclosures of whichare hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to providing instruments for the alignmentof an acetabular cup within the acetabulum, which may includepreoperative imaging to create a patient-specific guide for predefiningthe resection of the acetabulum to receive the acetabular cup.

The success of hip joint replacement surgery, which is a well-acceptedtreatment for arthritic conditions of the hip, depends upon preoperativeplanning and also the proper intraoperative placement of reamers,alignment instruments, and implants, for example, in order for thefunction of the joint to be optimized biologically and biomechanically.In particular, in hip replacement surgery, successful hip reconstructionis predicated upon restoring the biomechanics of the hip to “normal,” aswell as selecting implants of appropriate size to avoid intraoperativeor postoperative complications and to ensure long-lasting function.

The hip is a ball and socket joint. In the normal hip, the femoral headis generally circular and rotates within the acetabulum which is alsogenerally circular. Ideally, the stress transfer of body weight acrossthe hip joint is distributed across the surface area of the femoral headand acetabulum. A distribution of stress generally results in lowerstresses in the joint, as the maximum amount of surface area is beingused to distribute the stress.

In the diseased hip, the ball and socket may be malformed, and mayresult in an abnormally uneven distribution of stress. A deformedfemoral head, for example, one that is generally more oblong thancircular, will transfer stress from the femoral head to the acetabulumalong the periphery of the femoral head to the periphery of theacetabulum. This transfers the entire amount of stress, imported by thebody weight, to a much reduced surface area, thereby increasing thestress per unit area. The resulting increased stress per unit areagenerally damages the joint by damaging the articular cartilage, which,may wear out.

From a biomechanical standpoint, successful hip function depends onproper orientation of the muscles in relation to the center of rotationof the joint, such that leg length and offset are equalized followingsurgery. Surgery may be performed to restore the length of the leg toits original length, which in turn aims to restore the originalbiomechanics of the joint and thereby optimize function. A preoperativedetermination of the precise amount of the leg-length discrepancy, ifany, is necessary to correct the discrepancy intraoperatively andachieve leg-length equality, in other words, avoid over-lengthening orunder-lengthening of the leg.

In addition, restoration of hip function by performance of hipreplacement surgery depends upon reproduction of the femoral offset. Thefemoral offset is the distance from the center of rotation of the hipjoint to the longitudinal axis of the femoral shaft. The accuratedetermination of the femoral offset is important, because the femoraloffset determines the moment arm of the abductor muscles, in otherwords, how hard the muscles have to work. Therefore, in a surgical hipreplacement procedure, the offset needs to be restored appropriately forthe hip to function properly. If a hip prosthesis is installed withinsufficient offset because an acetabular component, for example, anacetabular cup, has not been properly positioned in the acetabulum, thehip muscles will have to generate increased force, which may lead todiscomfort and easy fatigability.

Alignment of an acetabular cup can be achieved with an alignment guidethat attaches to an insertion rod for facilitating the insertion of theacetabular cup into the acetabulum. The alignment guide preferablyreferences the surgical table on which the patient rests.Conventionally, it is assumed that the patient's pelvis is parallel tothe table, and that the surgical table is parallel to the floor. Basedon such assumptions, the ordinary position (in most patients) for theacetabular cup is 45° of inclination and 20° of anteversion. For adiscussion of angles of anteversion and also inclination or abduction ofthe acetabular cup when installed in the acetabulum, see, for example,U.S. Pat. No. 6,395,005, which is incorporated by reference herein inits entirety and is fully set forth herein.

It is has been found based on post-operative x-rays, however, thatdespite the alignment guide being parallel to the floor during insertionof the acetabular cup, the resultant inclination or anteversion of theacetabulum in relation to the alignment guide is often different thanexpected and, thus, the acetabular cup has been installed at a less thanideal position. In some circumstances, the inaccurate positioning of theacetabular cup may be caused by tilting of the pelvis of the patient inthe lateral decubitus position during the surgical procedure, whichtitling is not recognized during the procedure.

Some surgeons use intraoperative x-rays and navigation for detectingpelvic tilt intraoperatively. Intraoperative x-ray, however, is oftentime consuming and can potentially increase the risk of infection due tothe introduction of x-ray equipment into the operating theater. TheX-ray image, which is taken through the anterior/posterior (AP) view ofthe pelvis, typically is of poor quality and bony landmarks are oftenobscured, which makes accurate measurement of the pelvic tilt difficult.Also, although intraoperative x-rays may used to determine pelvic tilt,which in turn allows for a determination of the proper inclination ofthe acetabular component, the x-rays cannot provide information fromwhich the proper anteversion of the acetabular component can bedetermined.

In light of the above, there remains a need for a straightforward methodand system for the precise positioning of components relative to theacetabulum.

BRIEF SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention is apatient-specific guide used in hip arthroplasty and a method of creatingsuch a patient-specific guide. Preoperative images of a patient's pelvicregion are used in determining a patient-specific contact surface of theguide. The contact surface substantially matches the shape of at least aportion of the acetabulum such that the guide is stable once it isengaged to the acetabulum. The outer surface of the acetabulum whetherbone and/or cartilage that the contact surface of the guide isconfigured to engage is thus a negative of the contact surface of theguide.

With respect to the present aspect, the guide is generally used in hiparthroplasty procedures for patients with a deformed acetabulum due tobone degeneration and/or wear, for example. Instead of a generallycircular configuration, the deformed acetabulum is generally ovular.Even though the contact surface of the guide is patient-specific, it maystill be difficult to orient the guide in a correct preoperativelyplanned location because of the ovular configuration of the deformedacetabulum. Even if the guide is rotated in either a clockwise orcounterclockwise orientation while adjacent to the acetabulum, the guidewill not necessarily key into the correct preoperatively plannedlocation.

In accordance with the present aspect, the fovea of the acetabulum ispreferably used as an anatomical landmark to easily orient the guide inthe correct preoperatively planned position. Information relating to thelocation, size and shape of the fovea is analyzed in the preoperativeimages taken of the acetabulum. This information is used in order tocreate the patient-specific contact surface of the guide having afeature such as a protrusion on the contact surface of the guiderepresenting the negative of the fovea.

The fovea is an anatomical landmark that is unique to each patient. Thefovea is a recess or depression located generally at the bottom of theacetabulum. The fovea is generally shaped like an oval or horseshoe andis approximately one centimeter deep. The fovea is generally locatedalong a portion of the periphery of the acetabulum and extendsapproximately one-third of the acetabular floor toward the superior apexof the acetabulum. Because the fovea is shaped and located uniquely inevery individual, there are no two individuals who have identicallyshaped fovea in the same location relative to the deformed acetabulum.

In accordance with the present aspect, the guide further includes aguide slot. Preoperative images of a patient's pelvic region are alsoused in determining the location and orientation of the guide slot ofthe guide. The guide slot has an axis representing an insertional vectorof an acetabular component. During the preoperative planning of theguide, accurate acetabular component placement is generally firstdetermined. The polar axis of the acetabular component in the accuratelyplaced or implanted location and orientation is preferably co-linearwith the axis of the guide slot.

Once the optimal location of the acetabular component is determined inorder, for example, to correct a patient's deformity, the location andorientation of the guide slot of the guide may then be determined. Theguide slot of the guide is adapted to receive means for resecting bone.The bone resection means may be a rotating drill, for example. Once theguide is correctly positioned, a drill may be used to resect a portionof bone and/or cartilage of the acetabulum. After a portion of the boneand/or cartilage of the acetabulum is removed, the guide may then beremoved. A guide recess formed by the resection, the recess having anaxis co-linear with the polar axis of a correctly placed acetabularcomponent is now located in the bone of the acetabulum. This guiderecess is used to accurately locate a cutting tool such as a reamer, forexample, used to remove a sufficient amount of the bone of theacetabulum in order to repair the contact surface for the acetabularcomponent that will be engaged thereto. After the acetabulum is reamed,the acetabular component is accurately implanted in the acetabulum andaffixed thereto with a fastening means such as a screw, for example. Thescrew is positioned through a hole in the acetabular component and intothe guide recess previously formed by the guide slot of the guide. Alongitudinal axis of the hole is co-linear with the polar axis of theaccurately positioned acetabular component.

Another aspect of the present invention is a method of performing apreoperative plan for implanting a patient-specific acetabular implant.The method includes using three-dimensional (“3D”) imaging data of apelvic region of a patient. The image data is used to determine aninsertional vector for inserting an acetabular implant into anacetabulum of a hip of the patient, wherein the insertional vectorextends through a center of rotation of the hip of the patient. Themethod further includes constructing a 3D model of the acetabularimplant in relation to the insertional vector and the center of rotationof the hip, wherein the 3D model of the acetabular implant includes asuperior surface opposing the acetabulum and is shaped to substantiallymatch the shape of the acetabulum, wherein the superior surface definesa nub portion or protrusion shaped to substantially match the shape ofthe fovea of the acetabulum. The nub portion is positioned and orientedon the superior surface such that, when the acetabular implant obtainedfrom the 3D model is inserted into the acetabulum of the hip of thepatient with a center of rotation of the acetabular implant aligned withthe insertional vector, the nub portion can be received substantiallydirectly in the fovea of the acetabulum.

In one embodiment of the present aspect, the method further includesusing topographical landmarks of the pelvic region of the patientincluded in the 3D imaging data of the pelvic region to determine thecenter of rotation of the hip, and an anteversion angle and an abductionangle from which the insertional vector is determined.

In another embodiment of the present aspect, the constructing of the 3Dmodel of the acetabular implant includes using digital subtraction toshape the 3D model of the acetabular implant in relation to a contour ofthe acetabulum and the fovea.

In yet another embodiment of the present aspect, the method furtherincludes using the 3D imaging data to determine the center of rotationof the hip by positioning a digitized representation of a spheresubstantially centered within the acetabulum and sized for substantiallycontacting each of superior, inferior, anterior and posterior quadrantsof the acetabulum.

In yet still another embodiment of the present aspect, the sphere has amedial border disposed midway between an inner wall and an outer wall ofthe pelvis.

Another aspect of the present invention is a patient-specific acetabularimplant for insertion into an acetabulum of a hip of a patient. Theacetabular implant is obtained using a 3D model of the acetabularimplant and 3D imaging data of the pelvic region of the patient. Theimage data is used to determine an insertional vector for inserting theacetabular implant into the acetabulum of the hip of the patient,wherein the insertional vector extends through a center of rotation ofthe hip of the patient. The image data is further used to construct the3D model of the acetabular implant in relation to the insertional vectorand the center of rotation of the hip, wherein the acetabular implantincludes a superior surface to oppose the acetabulum and shaped tosubstantially match the shape of the acetabulum. The superior surfacedefines a protrusion or nub portion shaped to substantially match theshape of the fovea of the acetabulum, wherein the nub portion ispositioned and oriented on the superior surface such that, when theacetabular implant obtained from the 3D model is inserted into theacetabulum of the hip of the patient with a center of rotation of theacetabular implant aligned with the insertional vector, the nub portioncan be received substantially directly in the fovea of the acetabulum.

In one embodiment of the present aspect, topographical landmarks of thepelvic region of the patient included in the 3D imaging data of thepelvic region are used to determine the center of rotation of the hip,and an anteversion angle and an abduction angle from which theinsertional vector is determined.

In yet another embodiment of the present aspect, the 3D model of theacetabular implant is constructed using digital subtraction to shape the3D model of the acetabular implant in relation to a contour of theacetabulum and the fovea.

In yet still another embodiment of the present aspect, the center ofrotation of the hip is determined using the 3D imaging data bypositioning a digitized representation of a sphere substantiallycentered within the acetabulum and sized for substantially contactingeach of a superior, inferior, anterior and posterior quadrants of theacetabulum.

In yet still another embodiment of the present aspect, the sphere has amedial border disposed midway between an inner wall and an outer wall ofthe pelvis.

Another aspect of the present invention is a method of using apatient-specific guide in conjunction with a navigation system forpreparation and positioning of an acetabular component. Preoperativeimages of a patient's pelvic region are taken using computer tomography(“CT”), magnetic resonance imaging (“MRI”), or other imagingmethodology. The images are evaluated to determine the correct axis oforientation for the acetabular cup to achieve optimal range of motionfor a femoral component and maximum acetabular body coverage whileminimizing the reaction forces experienced in the acetabular cup. Theimage data is manipulated to create a patient-specific 3D model guidedepicting the unique negative impression of the contour of theacetabulum with a guide slot having an axis incorporated as a feature inthe model. The patient-specific guide may then be manufactured.

Intraoperatively, a patient is prepared in a standard manner for anavigated total hip arthroplasty procedure. Tracker pins may be placedin the iliac crest or other rigid area of the acetabulum. Incision ismade and the femoral neck is resected. The patient-specific guide isthen placed into the acetabulum. A navigated pointer may be insertedinto the guide slot or may alternatively be aligned with the prescribedaxis. The navigation system preferably registers the exact orientationand location including depth of the pointer relative to a globalcoordinate system created by the trackers. The patient-specific guidemay then be removed from the acetabulum. A navigated reamer handle andthen navigated cup inserter are used to prepare the acetabulum in thecorrect orientation based on the registered target.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will be apparentfrom the following detailed description of the present preferredembodiments, which description should be considered in conjunction withthe accompanying drawings in which like reference indicate similarelements and in which:

FIG. 1 is a block diagram of a system in accordance with an aspect ofthe present invention.

FIG. 2 is a flow diagram of a process in accordance with an aspect ofthe present invention.

FIG. 3 is an image of a portion of the pelvic region.

FIG. 4A is an image of a portion of the pelvic region including ananatomical landmark.

FIG. 4B is an image of the pelvic region including a pelvic axis.

FIGS. 5A and 5B are images of a portion of the pelvic region including avirtual representation of an acetabular component.

FIG. 6A is an image of a portion of the pelvic region including virtualrepresentations of acetabular components positioned in relation to theleft and right acetabulums, respectively.

FIG. 6B is the image of FIG. 6A including a pelvic axis.

FIG. 7 is an image of a portion of the pelvic region includinganatomical points in the anterior frontal plane of the acetabulum.

FIG. 8 is an image of a portion of the pelvic region for determininganteversion of the acetabular component.

FIG. 9 is a view of the right-side of a patient's pelvic region.

FIG. 10 is a perspective view of a patient-specific guide of the presentinvention.

FIG. 11 is another perspective view of the guide shown in FIG. 10.

FIG. 12 is an exploded view of a portion of a patient's pelvic regionand the guide shown in FIG. 10.

FIG. 13 is an assembled view of the features shown in FIG. 12.

FIG. 14A is a view of a navigated pointer inserted into a guide slot ofa patient-specific guide.

FIG. 14B is a view of a navigation system registering the orientationand location including depth of the pointer shown in FIG. 14A relativeto a global coordinate system created by trackers.

FIG. 14C is a view of a navigated reamer handle and navigated cupinserter being used to prepare the acetabulum in the correct orientationbased on the registered target.

FIG. 15 is a view of one embodiment of an acetabular component of thepresent invention having apertures through an outer circumferencethereof.

FIG. 16A is a view of one embodiment of a patient-specific guidepositioned in an acetabulum of a patient.

FIG. 16B is a view of the patient-specific guide shown in FIG. 16Awherein a guide pin is positioned through a guide slot of thepatient-specific guide.

FIG. 16C is a view of the guide pin shown in FIG. 16B guide thedirection of a cannulated reamer.

FIG. 17 is a view of one embodiment of an electronic device used torecord the position of a patient-specific guide positioned in anacetabulum of a patient.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a surgical guidance system 10, inaccordance with the present invention. Referring to FIG. 1, the system10 includes a computer 12 coupled to an imaging system 14, a navigationsystem 16 and an instrumentation guidance system 18. The system 10further includes an input device 20 and a display 22.

The imaging system 14 is a conventional imaging device for providingmedical images, such as X-rays, fluoroscopic, CT, MRI, etc., of apatient's anatomical regions.

The navigation system 16 is a conventional device including positionalsensors or trackers for attachment to a patient and surgical instrumentsfor reporting the location and orientation of the patient's anatomy anda surgical instrument in 3D space.

The computer 12 is a conventional processor including a memory andcapable of exchanging data and control signals with the imaging system14 and the navigation system 16 for obtaining images of the patient, andfor tracking data representative of the location and orientation of thepatient and surgical instruments in 3D space, respectively. See U.S.Patent Application Publication No. 2005/0203384, incorporated byreference herein.

The display 22 is a conventional device for displaying images obtainedby the imaging system 14, and virtual representations of a portion ofthe patient and a surgical or implant instrument in 3D space on an imageof the patent, where the virtual representations are based on dataobtained from the navigation system 16 or operation of the guidancesystem 18, in accordance with the present invention as discussed indetail below.

The input device 20 is a conventional data entry device, such as akeyboard, mouse, voice recognition system, etc. through which a user caninput data for performing operations related to determining apreoperative plan through use of the guidance system 18.

The guidance system 18, as discussed in detail below, includes aprocessor containing a memory and performs data processing operationsfor defining a preoperative plan for a surgical procedure in the pelvicregion of a patient using imaging data obtained by the imaging system,and for implementing the pre-operative plan in a surgical procedureusing tracking data obtained from the navigation system 16.

FIG. 2 is an exemplary process 50 for determining, based on images ofthe pelvic region of a patient, an insertional vector which can be usedto create a guide slot for a patient-specific acetabular guide or forthe positioning of a surgical instrument such as a navigated pointerduring a surgical procedure, in accordance with the present invention.As discussed below, the insertional vector determined from the process50 can be used to preoperatively plan a surgery in the pelvic region,such as a hip joint replacement surgery procedure, such that potentialcomplications can be identified and planned, and to increase the overallaccuracy of the surgically invasive operations, thereby reducing thepotential for intraoperative complications. The use of the insertionalvector intraoperatively assures accurate execution of the preoperativeplan.

For purposes of illustration, the process 50 is exemplified fordetermining an insertional vector for use in a total hip replacement,using a 3D reference coordinate system defined by X, Y, and Z axes,where a user interacts with the guidance system 18 via the input device20 and display 22 to define the reference coordinate system using imagesof the pelvic region of a patient obtained, such as by the imagingsystem 15.

Referring to FIG. 2, in block 52, the imaging system 14 may obtainimages of the patient's pelvic region and forward the image data to thecomputer 12, where the image data is stored in memory. In oneembodiment, the images are two-dimensional images, such as a radiograph.For example, x-rays are taken of the pelvic region, where the pelvicregion contains an existing implant of a known dimension. Alternatively,an x-ray of the pelvic region includes a radiographic marker of knowndimension that has been affixed adjacent to the pelvic region, externalto the patient. Referring to FIG. 3, a radiographic marker element Rhaving a known dimension between marker metal beads R1 and R2 can betaped to the skin of the patient at the level of the trochanter.

In one embodiment, the guidance system 18 retrieves the x-ray image datafrom the computer 12 and processes such image data, based on the knowndimensions of an object included in an image, for example, based on theknown distance between the beads R1 and R2 as shown in FIG. 3, todetermine whether the x-ray images have any magnification. The amount ofmagnification, if any, is stored in memory in the guidance system 18,and then used to correct for measurements made in other steps of theprocess 50 as discussed below. Thus, all measurements of distancesbetween objects in the images of the pelvic region processed as part ofthe process 50 are neither increased nor decreased artificially.

In an alternative embodiment, the imaging system 14 in block 52 obtains3D images of the pelvic region, which do not have any magnification, andforwards such images to the computer 12.

In block 52, the guidance system 18 receives data representative of thecoordinate reference system the imaging system 14 used when the imageswere obtained, which the imaging system 14 provided to the computer 12for use by the guidance system 18. The imaging coordinate referencesystem data provides the guidance-related reference coordinates, whichcorrespond to the locations of lines or points on a collected image thatmay be generated by use of the guidance system 18. This data can becorrelated to locations on a second collected image and provide thecorresponding lines or points on the second image which would bedeterminable and can be displayed on the second image at a correspondinglocation(s). For example, based on input received from the user at theinput device 20, a selected image of the pelvic region is displayed onthe display 22, and the guidance system 18 displays markings and axiallines, which are based on user inputs or the guidance system 18generates, superimposed on the displayed image.

In block 54, the user operates the guidance system 18 to identify apelvic axis (or X axis) and its orientation in the subject pelvicregion. The pelvic axis corresponds to an X axis as shown in FIG. 4B ofa guidance reference system, which can be used to determine aninsertional vector for performing a surgical procedure at the pelvicregion. The determination of the orientation of the pelvic axis for thepelvic region provides useful information for properly positioning asurgical instrument during a pelvic region surgical procedure because,oftentimes, the pelvis of a patient may be rotated or tilted during sucha procedure. In addition, the pelvic axis may be used as a referencepoint for measuring the length of a leg of the patient.

In one embodiment of the block 54, the user selects a collected 2D imageof the pelvic region for display and identifies with digital markings onthe image, such as by clicking a mouse, corresponding anatomicallandmarks on the left and right hips of the patient. For example, thelandmarks may include the acetabular teardrop 80 as shown in FIG. 4A,the ischial tuberosity the obturator foramen, or the greater sciaticnotch. When the displayed image is a conventional radiograph, a desiredand commonly used landmark is the acetabular teardrop (“TD”), which iscommonly visible on an image of an anteroposterior view of the pelvicregion as shown in FIG. 4A. Referring to FIG. 4B, the user digitallymarks the left (“Left TD”) and right (“Right TD”) acetabular teardrops82, 84 of the pelvic region on the image. The guidance system 18 thenautomatically inserts onto the image a line extending through the LeftTD and Right TD markings, and such line corresponds to the pelvic axisor X-axis of a reference coordinate system to be used in pre-operativeplanning. As discussed below, the pelvic axis can be used to determinethe appropriate abduction or inclination angle of an acetabularcomponent, such as the acetabular cup, with respect to a coordinatereference system, to provide acetubular components, such as included ina complete hip prosthesis, and desirably an acetabular cup, may beproperly and accurately positioned in the pelvic region of a patient.

In an alternative embodiment, 3D images may be used to define the pelvicaxis (X axis) in block 54. Referring to FIGS. 5A and 5B, the user, viathe guidance system 18, selects an image displayed on the displaycontaining the acetabulum region of a hip joint of the patient. Afterthe image is selected, the user operates the guidance system 18 togenerate digitally a virtual representation of a sphere 86 on the image.The user, with the input device 22, adjusts the size and position of thevirtual sphere, so as to superimpose the virtual sphere generally withinthe confines of the acetabulum of one of the hips. The user then furtheradjusts the position of the virtual sphere to position the spherecentrally within the acetabulum, and the size of the sphere so that itsouter surface touches the edge of all quadrants, e.g., superior,inferior, anterior, and posterior of the acetabulum, and the medialborder 90 of the sphere is positioned midway between the inner and outerwalls 92, 94 of the pelvis.

The user positions a virtual digital sphere 100 within the acetabulumfor each of the hips on the image, as shown in FIG. 6A. When the virtualspheres 100 have been appropriately sized and positioned within theacetabulums for the respective hips, the center of each of the spheres110, 120 corresponds to the center of rotation for the hip. Afterplacement of the virtual spheres 100 at the desired position within theacetabulums, the user enters an instruction at the input device 20,which indicates to the guidance system 18 that the sizing and thepositioning of the spheres has been completed. After the guidance systemreceives such indication, the guidance system 18 automatically generateson the image a line 130 extending through the centers Center-R 110 andCenter-L 120 of the virtual spheres 100 at the left and right hips,respectively, as shown in FIG. 6B, and such line 130 constitutes thepelvic axis (X axis) of the pelvic region.

In block 56, the user selects from the images collected by the imagingsystem 14 an image of the pelvic region from which the anterior frontalpelvic plane of the patient can be determined. Referring to FIG. 7,after the user selects an image, such as by providing a suitableindication using the input device 20, the guidance system 18 mayautomatically insert onto the selected image the pelvic axis previouslydetermined in block 54, at the corresponding location. The user, using amouse, digitally marks on the image reference points corresponding tothe left and right anterior superior iliac spines (“Left ASIS” 140 andRight ASIS” 150) and the pubic symphysis (“PS”) 160. After such pointsare digitally marked, the system 18 determines the points of a planecontaining these three reference points, and stores in its memoryinformation representative of the points of the plane for the image inrelation to the image reference system. Such plane constitutes theanterior frontal plane of the acetabulum for the left and right hips.

In block 58, based on the anterior plane data stored in memory, theguidance system 18 determines, and optionally displays on the image onwhich the anterior plane was defined, the coordinates of a line (“ASISline”) 170 connecting the Right ASIS to the Left ASIS, and thendetermines the coordinates of a point (“MP”) 180 on the ASIS linecorresponding to the midpoint. Further, the guidance system 18determines the coordinates of an axial line 190 extending through thereference point PS and the point MP, and optionally displays the line onthe image. Such axial line lies in the anterior plane and constitutesthe Y-axis of the guidance coordinate reference system. The Y-axiscorresponds to the frontal axis of the acetabulums of the left and righthips of the patient.

In block 60, the orientation of the acetabulum of a hip on which asurgical procedure is to be performed, in relation to the frontal axis,the pelvic axis and the pelvic plane of the pelvic region of thepatient, is determined. Based on the orientation determination, theorientation of a surgical instrument used in the surgical procedure forhip replacement, and also of an acetabular component to be inserted intoor in relation to the acetabulum, can be determined, to provide forprecision placement or movement of a surgical instrument or deviceduring the surgery. In one embodiment, the orientation of an acetabularcup, which is to be positioned within the acetabulum as part of a hipreplacement surgical procedure, is determined with respect to thereference axes and plane of the guidance coordinate system. Theorientation of the acetabular cup to be determined includes (i)inclination or abduction and (ii) anteversion.

To determine the inclination or abduction, the guidance system 18digitally generates a representation of an acetabular cup for one of thehips, for example, the left hip. The center of the cup is positionedinitially along the pelvic axis at the same location as the center ofthe digital sphere for the left hip from which the pelvic axis wasdefined. For ease of understanding, it is assumed that the virtual cupincludes a flat, circular surface and the surface is displayed initiallyco-planar with the anterior plane, with the center of the cup positionedon the pelvic axis at the same location as the center of rotation of thevirtual sphere for the left hip. The user, using the input device 20,rotates the cup about its center, away from the pelvic axis and in thefrontal plane, to determine an angle of inclination or abduction. Theuser observes the rotation of the cup on the display and continues toprovide for rotation of the virtual cup until the inclinationcorresponds to the inclination of the acetabulum for the left hip asshown on the image. The angle of rotation of virtual cup away from thepelvic axis is the angle of inclination, and the guidance system 18stores such information in its memory.

In one embodiment, after the guidance system 18 positions the virtualacetabular cup in relation to the pelvic axis with the center of thevirtual cup at the same point as the center of digital sphere for theacetabulum in which the cup is to be installed, the guidance system 18rotates the cup 45 degrees with respect to the pelvic axis and about itscenter of rotation, and then displays the virtual cup on the image withsuch inclination.

Further in block 60, the anteversion of the acetabular component isdetermined. In one embodiment, the user selects another image of theacetabulum of the left hip for display. After the user selects theimage, the user, with the input device, digitally marks reference pointson the acetabulum for use in determining the anteversion. For example,the reference points are the bone landmarks of the edge of the anteriorand posterior wall of the acetabulum, which correspond to the 3 o'clockand 9 o'clock position of the acetabulum. The user digitally marks suchreference points “3” and “9” on the image as shown in FIG. 8. Thenavigation system 16 provides that the user, using the input device 20,can cause the virtual cup to rotate about an axial line(“Inclination/Abduction axis”) extending in the frontal plane andpassing through the center of rotation of the cup. Such rotation of thevirtual cup corresponds to rotation in an anterior direction or withrespect to the Z axis of the guidance coordinate reference plane, sothat the edge of the virtual cup is tangent to the two points “3” and“9”, as shown in FIG. 8.

In one embodiment, the guidance system 16 automatically rotates thevirtual cup about the inclination/abduction axis 20 degrees, and storesinformation representative of such rotation in memory.

In block 62, the guidance system 16 determines the insertional angle orvector for a surgical instrument or surgical device, such as anacetabular component, based on the coordinate reference system definedin blocks using the pelvic and frontal axes and the frontal plane, andthe data representative of the inclination/abduction and anteversion ofthe acetabulum for such reference system, is determined.

The insertional vector is then used in preparing a pre-operative plan.In one embodiment, the insertional vector is used to define a guide slotin a patient-specific guide in order to accurately position anacetabular component, such as an acetabular cup, to be inserted into theacetabulum. The guide slot has an axis that is angled to correspond tothe insertional vector, and in particular has determined the correctlocation and position of the acetabular component (using the pelvic andfrontal axes as references). As every patient's anatomy is unique tothem, a custom mold of the patient's acetabular cavity will “key” intoposition in vivo. The mold will include an alignment reference whichwill recapitulate the preoperative plan. During final insertion of theprosthesis, the surgeon will reference the orientation of the shapefitting mold to assure accurate inclination and anteversion of theprosthetic component. In doing so, acetabular component alignment errorsdue to pelvic tilt and rotation during surgery will be eliminated.

The patient-specific total hip replacement insertional device is thencreated to mimic this insertional vector in vivo using topographicallandmarks unique to the patient. Using digital subtraction, the 3D imageremoves the femoral head and traces the contour of the patient'sacetabular bed, including the fovea. At the conclusion of steps onethrough seven, appropriate cup size, location, inclination, andanteversion will be determined. This is necessary in order toreestablish proper acetabular component position which is a prerequisitefor successful prosthetic reconstruction of the joint.

In one embodiment, preoperative images of a patient's pelvic region asshown in FIG. 9 are used in determining a patient-specific contactsurface 220 of guide 200 as shown in FIG. 10. The contact surface 220substantially matches the shape of at least a portion of the acetabulum300 such that the guide 200 is stable once it is engaged to theacetabulum 300. The outer or articular surface 320 of the acetabulumwhether bone and/or cartilage that the superior or contact surface 220of the guide 200 is configured to engage is thus a negative of thecontact surface 200 of the guide 200.

Guide 200 is generally used in hip arthroplasty procedures for patientswith a deformed acetabulum due to bone degeneration and/or wear. Insteadof a generally circular configuration, the deformed acetabulum isgenerally ovular. Even though the contact surface 220 of guide 200 ispatient-specific, it is still difficult to orient the guide in a correctpreoperatively planned location because of the ovular configuration ofthe deformed acetabulum. Even if the guide is rotated in either aclockwise or counterclockwise orientation while adjacent to theacetabulum, the guide will not necessarily key into the correctpreoperatively planned location.

The fovea 340 of the acetabulum is preferably used as an anatomicallandmark to easily orient the guide in the correct preoperativelyplanned position as shown in FIG. 13. Information relating to thelocation, size and shape of the fovea is analyzed in the preoperativeimages taken of the acetabulum. This information is used in order tocreate the patient-specific contact surface of the guide having afeature such as a nub portion or protrusion 280 as shown in FIG. 12 onthe contact surface of the guide representing the negative of the foveashown in FIG. 9.

Guide 200 further includes a guide portion 230 extending outwardly froman inferior surface 225 of guide 200. Guide portion 230 has a guide slot240 therethrough as shown in FIG. 11. Guide slot 240 has an axis 260representing an insertional vector of an acetabular component. Duringthe preoperative planning of the guide, accurate acetabular componentplacement is generally first determined. The polar axis of theacetabular component in the accurately placed or implanted location andorientation is preferably co-linear with the axis of the guide slot.

Once the optimal location of the acetabular component is determined inorder, for example, to correct a patient's deformity, the location andorientation of the guide slot of the guide may then be determined. Theguide slot of the guide is adapted to receive means for resecting boneas shown in FIG. 14A. The bone resection means may be a rotating drill,for example. Once the guide is correctly positioned, a drill may be usedto resect a portion of bone and/or cartilage of the acetabulum. After aportion of the bone and/or cartilage of the acetabulum are removed, theguide may then be removed. A guide recess formed by the resection, therecess having an axis co-linear with the polar axis of a correct placedacetabular component is now located in the bone of the acetabulum. Thisguide recess is used to accurately locate a cutting tool such as areamer as shown in FIG. 14C, for example, used to remove a sufficientamount of the bone of the acetabulum in order to repair the contactsurface for the acetabular component that will be engaged thereto. Afterthe acetabulum is reamed, the acetabular component is accuratelyimplanted in the acetabulum and affixed thereto with a fastening meanssuch as a screw, for example. The screw is positioned through a hole inthe acetabular component and into the guide recess previously formed bythe guide slot of the guide. A longitudinal axis of the hole isco-linear with the polar axis of the accurately positioned acetabularcomponent.

FIGS. 14A-C also depict a method of using a patient-specific guide 400in conjunction with a navigation system for preparation and positioningof an acetabular component. Preoperative images of a patient's pelvicregion are taken using CT, MRI or other imaging methodology. The imagesare evaluated to determine the correct axis of orientation for theacetabular cup to achieve optimal range of motion for a femoralcomponent and maximum acetabular body coverage while minimizing thereaction forces experienced in the acetabular cup. The image data ismanipulated to create a patient-specific 3D model guide as shown in FIG.14A depicting the unique negative impression of the contour of theacetabulum with a guide slot having an axis incorporated as a feature inthe model. The patient-specific guide may then be manufactured.

Intraoperatively, a patient is prepared in a standard manner for anavigated total hip arthroplasty procedure. Tracker pins 420 are placedin the iliac crest or other rigid area of the acetabulum. Incision ismade and femoral neck is resected. The patient-specific guide is thenplaced into the acetabulum. As shown in FIG. 14B, a navigated pointer440 is inserted into the guide slot or is alternatively aligned with theprescribed axis. The navigation system registers the exact orientationand location including depth of the pointer relative to a globalcoordinate system created by the trackers. The patient-specific guidemay then be removed from the acetabulum. As shown in FIG. 14C, anavigated reamer handle 460 and then navigated cup inserter 480 are usedto prepare the acetabulum in the correct orientation based on theregistered target.

The guide of the present invention may also be created without the useof preoperative imaging. While the exact configuration of the acetabulumof each individual is unique, the size and shape of the acetabulum of anindividual generally falls within a range of sizes and shapes.Therefore, a guide selected from a set of differently sized guides maybe used on a certain individual during a hip arthroplasty procedure.Each of the guides may also include a guide slot having an axisrepresenting the insertional vector of a corresponding acetabularcomponent. The insertional vector and/or contact surface of the guidemay be determined through antroprometric data of the acetabulum.

FIG. 15 shows an acetabular component, implant or cup 500 configuredwith apertures 502 oriented about an outer circumference 504 of the cupfor screw fixation. The cup shown includes apertures having a locationthat is preopertiavely determined. The location of the screws holes canbe preoperatively determined such that after the acetabular cup isimplanted in a predefined position within the acetabulum, the aperturesare located in a position wherein fixation means such as screws or thelike can secure the cup to the acetabulum without impinging on certainneurovascular structures. Also, the angles that the screws are insertedcan also be preoperatively determined based on the anatomy of thepatient.

Generally, the longer the screw, the more precisely it must be placed.If the acetabular cup is maloriented, then the apertures or holes aregenerally not in the proper position to insert the screws safely. Theacetabular cup shown allows for proper rotational alignment of the cupso that the holes are in a preferred position to insert screws safelyinto the pelvis without injury to neurovascular structures.

FIGS. 16A-C show, in part, one method of the present invention. As shownin FIG. 16A, patient-specific guide component 600 is positioned withinan acetabulum of a patient. Preferably, guide 600 is rotated about theacetabulum of the patient until a nub portion of the patient-specificguide is received by and is engaged to the fovea of the acetabulum ofthe patient.

As shown in FIG. 16B, after the patient-specific guide has beencorrectly positioned on the acetabulum, a guide recess 620 is created inthe acetabulum of the patient. Guide recess 620 is preferably created byguiding a guide pin 640 through a guide slot 610 of a guide portion ofthe patient-specific guide and into the acetabulum of the patient adesired distance from an articular surface of the acetabulum.

FIG. 16C shows patient-specific guide 600 being removed from the guidepin 640 located in the acetabulum and a cannulated reamer 650 placedover guide pin 640. Cannulated reamer preferably rotates about guide pin640 while translating in a proximal direction in order to resect thearticular surface of the acetabulum. Preferably, reamer 650 resects theacetabulum until the reamer travels in the proximal direction thedesired distance. In some instances, reamer 650 may travel in theproximal direction more or less than the desired distance based ondecisions made by the surgeon.

After resecting the acetabulum with reamer 650, the reamer and guide pin650 are removed and an acetabular implant is preferably implanted in theresected acetabulum. Preferably, the acetabular implant has a polar axiscoaxial with a longitudinal axis of the guide recess created in theacetabulum by the guide pin.

FIG. 17 shows one embodiment of an electronic device 760 used to recordthe position of a patient-specific guide 700 positioned in an acetabulumof a patient. This embodiment, uses Global Positioning System (“GPS”) orlike technology to capture the position of guide 700 such that thisinformation may be used to recreate the position of an insertionalvector, for instance, on trials and implants later on.

Once guide 700 is correctly positioned in the acetabulum, an electronicmeasurement may be taken by electronic device 760 of the exactinsertional vector or angle in space defined by a guide slot in guide700, for example. This measurement or “snapshot” preferably serves as abaseline orientation and can be used in subsequent steps, e.g., reamingand acetabular component insertion, in order to reproduce theinsertional angle derived from guide 700.

The value of this measurement comes in the fact that once reaming of theacetabulum begins, guide 700 will no longer fit into the acetabulum inits preoperatively planned position and therefore can no longer serve asa reference for orientation. This technology may be incorporated into apersonal digital assistant (“PDA”) such as the iPhone, for instance. Inone embodiment, an application for use with a PDA may be used to measurethe insertional vector in space as described above. As shown in FIG. 17,once electronic device 760 is attached to the a guide inserter 720 viaan extension element 740, the position of the insertional angle may beset. During reaming and cup insertion, an iPhone (or other similar PDAdevice) is attached to a reamer handle or cup inserter 720 and theinsertional angle is remeasured. At this point, the reamer handle or cupinserter position can be readjusted to match the original position whichwas set by guide 700.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention.

1. A patient-specific guide comprising: a superior surface shaped tosubstantially match a socket joint of a patient; an extension portionprojecting outwardly from the superior surface to stabilize thepatient-specific guide in the socket joint; and a guide portionextending outwardly from an inferior surface, the guide portion havingan aperture with a longitudinal axis that aligns with a rotational axisof a corresponding joint component, wherein the extension portion isshaped to substantially match the shape of anatomical features of thesocket joint adjacent a rim of the socket joint, and wherein theextension portion is shaped such that when the extension portion engagesthe anatomical features, the guide is located in a preoperativelyplanned position and orientation with respect to the socket joint. 2.The guide of claim 1, wherein the superior surface is generally convex.3. The guide of claims 2, wherein the extension portion is generallyconvex and has a greater convexity in at least one direction than thatof the superior surface.
 4. The guide of claim 1, wherein the extensionportion is shaped such that the guide may be rotated about the socketjoint until being received in a recess adjacent a periphery of thesocket joint to confirm the preoperatively planned position andorientation.
 5. The guide of claim 1, further comprising a planar endsurface intermediate the superior and inferior surfaces thereof.
 6. Theguide of claim 5, wherein the guide portion extends outwardly from theinferior surface such that at least a portion thereof is locateddistally of a plane defined by the planar end surface.
 7. The guide ofclaim 1, wherein the guide portion has inner and outer wall surfaces anda distal end surface intermediate the inner and outer surfaces thereof.8. The guide of claim 7, wherein the distal end surface of the guideportion is planar.
 9. The guide of claim 1, wherein the guide portion iscylindrically shaped.
 10. The guide of claim 1, wherein the inferiorsurface of the guide is generally concave.
 11. A patient-specific guidecomprising: a superior surface shaped to substantially match a socketjoint of a patient; an extension portion projecting outwardly from thesuperior surface to stabilize the patient-specific guide in the socketjoint; and a guide portion extending outwardly from an inferior surface,the guide portion having an outer wall and an inner wall, the inner wallforming a slot having a longitudinal axis that aligns with a rotationalaxis of a corresponding joint component, wherein the extension portionis shaped to substantially match the shape of anatomical features of thesocket joint adjacent a rim of the socket joint, and wherein theextension portion is shaped such that when the extension portion engagesthe anatomical features, the guide is located in a preoperativelyplanned position and orientation with respect to the socket joint. 12.The guide of claim 11, wherein the superior surface is generally convex.13. The guide of claims 12, wherein the extension portion is generallyconvex and has a greater convexity in at least one direction than thatof the superior surface.
 14. The guide of claim 11, wherein theextension portion is shaped such that the guide may be rotated about thesocket joint until being received in a recess adjacent a periphery ofthe socket joint to confirm the preoperatively planned position andorientation.
 15. The guide of claim 11, further comprising a planar endsurface intermediate the superior and inferior surfaces thereof.
 16. Theguide of claim 15, wherein the guide portion extends outwardly from theinferior surface such that at least a portion thereof is locateddistally of a plane defined by the planar end surface.
 17. The guide ofclaim 11, wherein the guide portion has inner and outer wall surfacesand a distal end surface intermediate the inner and outer surfacesthereof.
 18. The guide of claim 17, wherein the distal end surface ofthe guide portion is planar.
 19. The guide of claim 11, wherein theguide portion is cylindrically shaped.
 20. The guide of claim 11,wherein the inferior surface of the guide is generally concave.